In orthopaedics, for several years a technique has been known for stabilising fractures without using external fixators instead of conventional plaster casts.
External fixators usually comprise a plurality of bone screws, normally in pairs, which are implanted in the bone fragments of the fracture in such a way that the head ends of the screws project from the skin of the patient. Said ends are anchored to a rigid external frame which is equipped with clamps and joints which can be orientated in such a way as to allow them to be adjusted to the position of the screws.
The screws usually have a cylindrical body, delimited on one side by a threaded end designed to be screwed into the bone fragment, and on the other side by the above-mentioned head end, which is shaped in such a way that it can be connected to a temporary grip which allows the screw to be screwed into the bone fragment. The connection between the screw and the grip is normally of the male-female type with quick coupling and release.
When operating, after making an incision in the soft tissue, the surgeon makes holes in the bone fragments on opposite sides of the fracture fissure and implants the screws in the holes. Then the surgeon connects the screw, without the temporary grip attached, to the respective clamps of the frame. If necessary, the surgeon then performs an operation called “reduction”, that is to say, with the aid of radiological equipment (luminance amplifier) he aligns the edges of the fracture in such a way as to arrange the bone fragments in the most suitable position to knit together.
Once the fracture has been reduced, the surgeon locks the joints and clamps to hold the bone fragments in the predetermined position, thus allowing the correct formation between the bone fragments of “bone callus”, which gradually restores the lamellar bone tissue with which the bone recovers its original continuity and functionality.
With a hold on the bone far from the centre of fracture and with stabilisation and adjustability outside of the fracture, external fixators allow action on the bone fragments whilst at the same time leaving the fracture zone free for surface medication.
Moreover, external fixators do not interfere with the airing of the fractured part and they prevent the loss of muscle tone normally encountered with the use of plaster casts.
Several years ago, the use of external fixators was extended to a vast range of orthopaedic operations, such as limb lengthening, correction of bone axis rotary and angular deformities, pseudarthrosis, etc. In other words, external fixators are today used as multi-purpose orthopaedic devices, both to correct deformations caused by trauma and to correct pathological deformations.
However, the prior art external fixators are not without disadvantages.
One disadvantage is the fact that in order to implant the bone screws, that is to say, to screw them in, an additional accessory has to be used, in the form of the above-mentioned temporary grip. Obviously, that adds complexity to the operations to be performed, as well as significantly extending the time required, due to the need to connect and then disconnect the temporary grip to and from each screw.
Another disadvantage is limited versatility and discomfort during use.
It should be remembered that the position of the screws is constrained by the presence of muscles, blood vessels, nerves and other soft tissue. When possible, the screws are implanted in such a way that they pass through “safe corridors” in the soft tissue and, therefore, they can emerge from the skin of the patient at various angles and lying in various planes. In practice, it was found that arranging the screws at various angles is more effective for stabilising the fracture.
In prior art external fixators, in particular in those in which the frame has one or more rigid bars which are connected to each other by clamps and joints, the choice of the above-mentioned angles is rather limited, or the desired angles are difficult to achieve with just a few rapid adjustments.